The research will apply a combination of anatomical (dye-injection, degeneration) and physiological (microelectrode recording) methods to examine the relationship between specific mechanosensory axons and identified interneurons that participate in the crayfish escape response. The topographic relationship between receptors, their axons, and central elements will be explored as a prelude to an analysis of the specificity of regeneration and, ultimately, of development de novo. We will inquire whether there is topographic segregation of input on the dendritic tree of postsynaptic cells, and investigate the nature of connection specificity already demonstrated for directionally selective afferents. The mechanism of presynaptic inhibition exerted on the afferent endings by command pathways will be investigated by studies using sucrose-gap recording from sensory nerves; both the pharmacology and ionic dependence of primary afferent depolarization will be studied. Experiments using the muscle receptor organ afferents will test the degeneration time and the reestablishment of central connections by identified sensory nerves, and this system may also be developed for studies on presynaptic inhibition. Finally, studies on abdominal neuromuscular systems will attack the basis for low-frequency depression of junctional potentials, and the basis for quantal release in a phasic junction.